BR112016001777B1 - REACTOR SYSTEM FOR THE FERMENTATION OF A GASEOUS SUBSTRATE, AND METHODS TO IMPROVE THE MASS TRANSFER OF A GASEOUS SUBSTRATE AND TO REDUCE FOAM IN THE UPPER SPACE OF A FERMENTATION BOWL - Google Patents

Abstract

reactor system for the fermentation of a gaseous substrate, and, methods for improving the mass transfer of a gaseous substrate and for reducing foam in the head space of a fermentation vessel. a reactor system is provided for better fermentation of a gaseous substrate by introducing a secondary loop to a forced circulation loop reactor. the reactor comprises a primary cycle through which fermentation broth comprising a gaseous substrate is circulated through a riser segment and a falloff section by a cycle pump. downstream of the cycle pump a portion of the fermentation broth is withdrawn from the descending section and is directed to the top of the reactor through a secondary cycle. further provided is a method for improving mass transfer from a gaseous substrate to a fermentation broth in a fermentation vessel comprising a secondary cycle. further provided is a method for reducing foam in the headspace of the fermentation vessel comprising a secondary cycle.

Description

FIELD OF THE INVENTION

[001] The invention relates to systems and methods for improving a forced circulation external cycle reactor. In particular, the invention introduces a secondary loop for an external forced circulation loop reactor that regulates gas retention in the reactor and allows for better foam control.

FUNDAMENTALS OF THE INVENTION

[002] Fuels and chemical substances produced by the synthesis of gas (singas) or industrial off-gas containing CO represents a main alternative to fossil fuel and chemical substances derived from it. Chemical catalytic conversion of these gases to fuels or chemicals is expensive or commercially unattractive. Instead, the biological conversion of these gases into fuels and chemicals (known as gas fermentation), has several advantages over catalytic processes, including greater specificity, higher yields, lower energy costs and greater resistance to poisoning.

[003] The efficiency of gas fermentation is known to be primarily limited by a low mass transfer rate of liquid gas due to the low solubility of gaseous substrates (eg CO and H2) in liquids. Mass transfer efficiency, or volumetric mass transfer rate, is given as follows:

[004] Where is the rate at which the gaseous substrate is transferred to the liquid phase; kLa is the volumetric mass transfer coefficient, it consists of the net lateral mass transfer coefficient kL and the specific mass transfer surface area, a. C* is the saturation concentration of the gas in the liquid (ie the solubility) which is proportional to the partial pressure of the gaseous substrate and CL is the actual gas concentration in the liquid, the difference between the two, ie (C* - CL) is the mass transfer driving force. Under limited conditions of pure mass transfer, CLÃ20"VR is the wet volume of the reactor and is the sum of the gas volume and the net volume.

[005] Therefore, in order to improve the mass transfer efficiency, it is necessary to increase the kLa or the driving force. The driving force can be improved by using high pressure; however, such methods are costly as gas compression is required. It is generally more preferred to increase the kL and/or a. While kL is an intrinsic property of liquid and gas, meaning that it is difficult to change, a has a simple relationship to gas retention, iG, and the mean bubble radius, rb, both of which can be easily manipulated. The relationship is as follows:

[006] The above equation dictates that the specific mass transfer area can be increased by an increase in gas retention, iG, or decrease in bubble size, rb, or a combination of both. Unfortunately, most such methods tend to generate a large amount of foam, which can block pipelines downstream of the bioreactor. Therefore, when measures are taken to increase the mass transfer surface area, special attention must be paid to foam control.

[007] A high mass transfer rate is generally desirable for gas fermentation. However, the process can suffer from substrate inhibition if the mass transfer rate is greater than the maximum reaction rate the microbes can provide. For example, a high concentration of dissolved CO results in slow growth of microbes and slow uptake of H2, and if such conditions last for an extended period of time, the culture may slowly die out (Design of Bioreactors for Coal Synthesis Gas Fermentations, JL Vega, EC, Clausen and JL Gaddy, 1990, Resources, Conservation and Recycling, Vol 3, Pages 149-160; Effect of CO partial pressure on cell-recycled continuous CO fermentation by Eubacterium limosum KIST612, IS Chang, BH Kim, RW Lovitt , JS Bang, 2001, Process Biochemistry, Vol 37, Page 411-421). Such eqpfk>õgu fg "uwrgtcdcuVgekogpVq" rqfgo qeqttgt inqdcnogpVg go wo tgcVqt small scale, well mixed, but can also occur in a large scale reactor where there is a high concentration of local dissolved CO, typically at the bottom where the gas is introduced and the partial pressure of CO is high.

[008] Therefore, a commercial scale reactor for gas fermentation needs to provide a high gas-to-liquid mass transfer rate, and it also needs to be flexible so that the mass transfer rate can be regulated when necessary. Effective foam control is also a requirement.

[009] At bench scale, gas fermentation is typically conducted in continuous stirred tank reactors (CSTR). However, these are unsuitable for commercial scale application due to high energy consumption and other issues. Instead, bubble columns with or without internal or external cycles can be used for large-scale gas fermentation. Forced circulation external loop reactors are a type of bubble column reactor in which the liquid is forced to circulate between a main (upward) column and an external (downward) loop by a pump, herein referred to as a cycle pump. .

[0010] In known forced circulation cycle reactor configurations, the speed of the cycle pump has two main effects on the hydrodynamics and mass transfer of the system: (a) an increase in the speed of the cycle pump increases the gas carryover of the climb to descent, which tends to increase the climb and retain the descent and therefore improves mass transfer; (b) an increase in cycle pump speed increases liquid velocity on ascent, which tends to erode gas bubbles on rapid ascent and decreases gas retention and reduces gas residence time. Conversely, if the pump cycle speed is reduced, the rising gas bubbles can stay for a long period of time, but the gas drag within the descent will be substantially less, which could reduce the descent reaction rate and the overall reactor performance. In addition, as the gas introduced at the bottom of the ascent has a higher CO content, a low cycle pump speed in a deep reactor aggravates substrate inhibition.

[0011] Therefore, a cycle pump is ineffective in terms of regulating mass transfer due to its competitive effects on gas drag and liquid velocity on ascent. It is an object of the present invention to provide a means to decouple the racing effects of the cycle pump and provide more effective mass transfer regulation here, as well as better foam control and lower overall energy consumption. Furthermore, the present invention overcomes disadvantages known in the art and provides the public with new methods for optimally producing a variety of useful products. Even small improvements to a gas fermentation process or system for producing one or more products can have a significant impact on the efficiency and, more particularly, the commercial viability of such a process or system.

SUMMARY OF THE INVENTION

[0012] In a first aspect, there is provided a reactor system for the fermentation of a gaseous substrate, the system comprising: (a) A fermentation vessel comprising a riser section in which a liquid fermentation broth and the gaseous substrate are fluids concurrently upwards and a descending section in which the liquid fermentation broth and gaseous substrate are concurrently flowing downwards, said ascending and descending sections connected by substantially horizontal sections and configured so that the liquid fermentation broth and the gaseous substrate are circulated, using pumping means, in a primary cycle from a point near the bottom of the descending section, through the ascent to an entry point at the top of the descending section; at a point near the bottom of the ascent section, piping means connecting the outlet from the bottom of the ascent section to an inlet at the top of the ascent and means for pumping located between the exit point and the entry point so that the fermentation broth and gaseous substrate are circulated from the bottom of the descent to the top of the riser section; (c) At least one gas inlet, configured to direct the gaseous substrate within the riser section; and (d) At least one gas outlet, configured to let gas exit the ascent section.

[0013] In particular embodiments of the first aspect, the bioreactor is configured for the fermentation of a gaseous substrate to produce products comprising at least one acid or alcohol or mixture thereof. In particular embodiments, the gaseous substrate comprises CO and optionally H2. In still alternative embodiments, the gaseous substrate comprises CO2 and H2.

[0014] In particular embodiments of the first aspect, the reactor comprises a primary cycle, which is comprised of a rise section and a fall section, and a secondary cycle. In particular embodiments, the secondary cycle removes fermentation broth from the descending section of the fermentation vessel. In particular embodiments, the secondary cycle removes fermentation broth from the descent of the primary cycle pump. In particular embodiments, fermentation broth is withdrawn downstream of the primary cycle pump by means of a secondary pump.

[0015] In alternative embodiments, the fermentation vessel descending section comprises a gate valve located upstream of the secondary loop outlet. In this modality, fermentation broth can be withdrawn from the descent section to the secondary cycle by restricting the flow of the primary cycle using a gate valve. By adjusting the gate valve opening, the pressure downstream of the cycle pump but upstream of the gate valve can be regulated to provide a desired secondary cycle flow rate. In certain modalities, the descent pressure is monitored by a pressure gauge. This configuration eliminates the requirement for a secondary cycle pump.

[0016] In particular embodiments, the removal of fermentation broth from the descent section is circulated through the secondary cycle at the top of the fermentation vessel. In particular embodiments, the fermentation broth and gaseous substrate are circulated through a secondary cycle from the smallest portion of the descending section to the top of the rising section. In particular embodiments, fermentation broth exits the secondary cycle from at least one nozzle at the top of the fermentation vessel. In use, the at least one nozzle sprays the fermentation broth circulated into the headspace of the fermentation vessel. In particular embodiments, the circulated fermentation broth is sprayed into the headspace by multiple nozzles. In particular embodiments, the at least one nozzle is a shower head. In particular embodiments, the velocity of the liquid jet or jets exiting the nozzle or nozzles can vary from about 0.5 m/s or to about 5 m/s. In use, the liquid jet or jets cover at least a portion of the cross-sectional area of the headspace. Under typical fermentation conditions, a layer of foam exists in the head space of the fermentation vessel. In certain embodiments, the circulated fermentation broth is sprayed into the headspace in order to break large bubbles in the foam. This process results in smaller bubbles that are more efficiently drawn into the descending section, which increases gas retention in the descending section.

[0017] In a particular modality, the secondary cycle is integrated with a cell recycling system. In this mode, the driving force for the secondary cycle is derived from a cell recycle pump. In a particular embodiment, the fermentation broth is taken from the secondary cycle downstream of the cell recycle module. In particular embodiments, the secondary cycle flow rate and pressure of the cell recycling system are regulated by at least one valve control upstream of the cell recycling module.

[0018] In a second aspect of the invention, a method is provided for improving mass transfer from a gaseous substrate to a fermentation broth in a fermentation vessel comprising a riser section in which a liquid fermentation broth and the gaseous substrate are fluid concurrently upwards and a run-down section wherein the liquid fermentation broth and the gaseous substrate are fluid concurrently on run-down, the method comprising: (a) providing a gaseous substrate to the fermentation vessel comprising a liquid nutrient medium and a or more microorganisms; (b) ferment the gaseous substrate to produce a fermentation broth; (c) circulate the fermentation broth and the gaseous substrate concurrently up through the riser section and concurrently down through the falloff section of the fermentation vessel; and (d) removing at least a portion of the fermentation broth from the bottom of the riser section and circulating to the top of the riser section through a secondary cycle, in which the fermentation broth enters the top of the riser section through hair. minus one mouthpiece.

[0019] In a third aspect of the invention, a method for reducing foam in the headspace of the fermentation vessel is provided comprising a riser section in which the liquid fermentation broth and the gaseous substrate are concurrently flowing upward and a section of in which the liquid fermentation broth and the gaseous substrate are flowing down concurrently, the method comprising: (a) providing a gaseous substrate to the fermentation vessel comprising a liquid nutrient medium and one or more microorganisms; (b) fermenting the gaseous substrate to produce a fermentation broth and foam present in the headspace of the fermentation vessel; (c) removing the fermentation broth from the descending section of the fermentation vessel; and (d) circulating the fermentation broth to the top of the riser section through a secondary cycle, wherein the fermentation broth enters the headspace through at least one nozzle; wherein the fermentation broth entering the headspace reduces the foam present inside the fermentation vessel.

[0020] In a fourth aspect, a method of producing products by fermenting a gaseous substrate is provided, the method comprising: (a) providing the gaseous substrate to a reactor comprising at least a riser section and a falloff section, the reactor containing a liquid nutrient medium and a culture of one or more microorganisms to provide a fermentation broth; (b) circulate the fermentation broth and gaseous substrate concurrently up through the riser section and then down through from the descent section; (c) remove at least a portion of the fermentation broth from the descent section and pass it to the top of the climb section; and (d) anaerobically fermenting the culture in the reactor to produce one or more products from said substrate.

[0021] In particular embodiments of the second, third and fourth aspects, the reactor is configured as described in the first aspect. In particular embodiments, the method allows for increased mass transfer from gas to the liquid phase in a gas fermentation process. In particular embodiments, the addition of a secondary loop to a looped loop reactor substantially increases mass transfer.

[0022] In particular modalities, the fermentation broth and the gaseous substrate are cycled through the rise section and a fall section of a looped cycle reactor. In particular embodiments, the gas stream enters the top of the reactor riser section. In alternative embodiments, the gas enters multiple sites through the riser section of the reactor. In alternative embodiments, the gas enters multiple sites through the descent section of the reactor.

[0023] In particular embodiments, a portion of the fermentation broth is withdrawn near the bottom of the reactor down-section section and circulated to the upper space of the reactor up-section section. In particular embodiments, the portion of the fermentation broth removed from the outlet is sprayed into the head space of the rise through a shower head or perforated nozzle. In certain embodiments, the liquid sprayed into the headspace reduces the foam layer on top of the liquid contained in the rise. In other embodiments, the liquid sprayed into the headspace breaks foam bubbles and entrains the gas within the primary loop fermentation broth of the reactor.

[0024] In particular embodiments, one or more microorganisms ferment the carbon-containing substrate to produce products including acids and alcohols. In particular embodiments, the one or more microorganisms produce one or more products by fermenting a gaseous substrate comprising CO. In particular embodiments, fermentation is anaerobic fermentation. In particular embodiments, the one or more cultures of microorganisms convert CO and optionally H2 to products including acids and/or alcohols. In particular embodiments, products are selected from the group consisting of ethanol, acetic acid, 2,3-butanediol, butanol, lactate, succinate, methyl ethyl ketone (MEK), propanediol, 2-propanol, isopropanol, acetoane, iso-butanol , citramalate, butadiene, polylactic acid, isobutylene, 3-hydroxy propionate (3HP), acetone, fatty acids and mixtures thereof.

[0025] In various embodiments, fermentation is conducted using a microorganism culture comprising one or more carboxydotrophic bacterial strains. In various embodiments, carboxydotrophic bacteria are selected from Clostridium, Moorella, Oxobacter, Peptostreptococcus, Acetobacterium, Eubacterium, or Butryribacterium. In one embodiment, the carboxydotrophic bacteria is Clostridium autoethanogenum. In particular modalities, the bacterium has the identification characteristics of the accession number DSMZ10061 or DSMZ23693.

[0026] The gaseous substrate may comprise a gas obtained as a by-product of an industrial process. In certain embodiments, the industrial process is selected from the group consisting of ferrous metal manufacturing products, non-ferrous manufacturing products, refining processes, petroleum refining processes, biomass gasification, coal gasification, electricity production, production black coal, ammonia production, methanol production and coca manufacturing. Alternatively, the gases substrate is a source of reformed gas including natural gas, shale gas, associated petroleum gas and biogas. In alternative modalities, the gas is obtained by gasification of biomass or municipal solid waste. In one embodiment of the invention, the gaseous substrate is singas. In one embodiment, the gaseous substrate comprises a gas obtained from a steel mill.

[0027] The invention also includes the parts, elements and characteristics referred to or indicated in the order specification, individually or collectively, in any or all combinations of two or more of said parts, elements or characteristics, and in which specific integers are mentioned herein that have known equivalents in the art to which the invention is related, such known equivalents are considered to be incorporated herein as if set out individually.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The invention will now be described in detail with reference to the attached Figures in which:

[0029] Figure 1 shows a schematic diagram of an embodiment of a looped loop reactor comprising a secondary loop.

[0030] Figure 2 shows a schematic diagram of an alternative embodiment of the looped loop reactor comprising a gate valve, eliminating the need for a secondary pump.

[0031] Figure 3 shows a schematic diagram of an embodiment of the looped cycle reactor comprising an integrated cell recycling system, eliminating the need for a secondary pump.

[0032] Figure 5 is a graph showing the effect of secondary pump flow rate on rise retention based on experimental results from a 6 meter high reactor.

[0033] Figure 6 is a graph showing the effect of the secondary cycle on CO conversion based on experimental results from a 6 meter high reactor.

[0034] Figure 7 is a graph showing the effect of a secondary cycle on climb retention based on experimental results from a 3 meter high reactor.

[0035] Figure 8 is a graph showing the effect of secondary cycle pump speed on climb and hold on descent based on experimental results from a 10 meter high reactor.

[0036] Figure 9 is a graph showing the effect of the speed of a secondary cycle pump on the CO conversion, based on experimental results from a 10 meter high reactor.

DETAILED DESCRIPTION OF THE INVENTIONDefinitions

[0037] Unless otherwise defined, the following terms as used throughout this specification are defined as follows:

[0038] Q Vgtoq "uwduVtcVq icuquq" kpenwk swcnswgt iáu swg eqpVwire wo compound or element used by a microorganism as a carbon source and optionally as a source of energy in fermentation. The gaseous substrate will typically contain a significant proportion of CO, from at least about 5% to about 100% CO by volume.

[0039] Although it is not necessary for the substrate to contain any hydrogen, the presence of H2 should not be detrimental to the formation of the product according to the methods of the invention. In particular embodiments, the presence of hydrogen results in an overall improvement in the efficiency of alcohol production. For example, in particular embodiments, the substrate can comprise a ratio of about 2:1, or 1:1, or 1:2 H2:CO. In particular embodiments, the substrate can comprise a ratio of between 2:1 to 1:2 H2:CO. In one embodiment, the substrate comprises about 30% or less H2 by volume, 20% or less H2 by volume, about 15% or less H2 by volume, or about 10% or less H2 by volume. In other embodiments, the substrate stream comprises low concentrations of H2, for example, less than 5%, or less than 4%, or less than 3%, or less than 2%, or less than 1%, or is substantially free of hydrogen. The substrate may also contain some CO2, for example, such as about 1% to about 80% CO2 by volume, or 1% to about 30% CO2 by volume. In one embodiment the substrate comprises less than or equal to about 20% CO2 by volume. In particular embodiments, the substrate comprises less than or equal to about 15% CO2 by volume, less than or equal to about 10% CO2 by volume, less than or equal to about 5% CO2 by volume, or substantially no CO2.

[0040] Q Vgtoq "oekq PwVtkgpVg niswkfq" kpenwk wo ogkq niswkfq comprising nutrients suitable for fermentation of one or more microorganisms. The liquid nutrient medium will contain enough vitamins and/or minerals to allow the microorganisms used to grow. Suitable anaerobic media for fermentation using CO are known in the art. For example, suitable means are described in Beibel (Journal of Industrial Microbiology & Biotechnology (2001) 27, 18-26).

[0041] Q Vgtoq "áekfq" eqoq wVükzcfq cswk kpenwk codqu áekfqu carboxylates and the associated carboxylate anion, such as the mixture of free acetic acid and acetate present in a fermentation broth as described herein. The ratio of molecular acid to carboxylate in the broth of fetogpVc>«q fi fepgpfgpVe fq pH fq ukuVgoCo Go cfk>«q. q Vgtoq “ceeVcVq” includes both the acetate salt alone and a mixture of free acetic acid molecules and the acetate salt, such as the mixture of the acetate salt and free acetic acid present in the fermentation broth as described herein.

[0042] Qu Vgtoqu "teekrkepVe fg fetoepVc>«q", "tecVqt" glqw "dkqttecVqt" kpenweo fkurqukvkxqu and teekrkepVeu rctc q eqpVcVq iáuiníswkfq, suitable for conducting the desired fermentation.

[0043] Wo "tecVqt fe ekenq ezVetpq fe ektewnc>"q forçcfc" elqw "tecVqt fe ekenq ektewncfq" eqorteepfe wo teekrkepVe pqtocnoepVe Vepfq fqku vertical cylinders with horizontal connections between them. The content, which is usually a liquid plus a substrate gas, is forced to circulate up a vertical cylinder (upward) through a horizontal connection and then down through another vertical cylinder (downward) and then through a horizontal connection lower reactor by an impeller or a pump of an appropriate type to complete the cycle.

[0044] Q Vetoq “uwdkfc” eqorteepfe woc ue>«q fq tecVqt and the swe q liquid/gas content runs concurrently upwards.

[0045] Q Vetoq “feuekfc” eqorteepfe woc ue>«q fq tecVqt and the swe q liquid/gas content runs concurrently downwards.

[0046] Q Vetoq “uerctcfqt” kpenwk c re>c fq tecVqt and the swe renq minus a portion of the gas separates from the liquid-gaseous two-phase mixture allowing the bubbles to rise to the surface of the liquid.

[0047] Q “eurc>q uwretkqt” kpenwk c rctVe fq tecVqt cekoc fq separator defined above.

[0048] Q Vetoq “dqodc fe ekenq” eqorteepfe woc dqodc swe fi used to direct the liquid medium in the reactor to flow. The liquid medium may contain a certain amount of gas bubbles or dissolved gas. In a particular embodiment, this may include an axial flow pump installed at the bottom of the descent.

[0049] Q Vetoq “dqmfafqt” and elqw “fkuVtkdwkfqt fe iáu” eqorteepfe a device for introducing gas into a liquid to agitate it or to dissolve the gas in the liquid. In a particular embodiment, the spray can be a perforated plate, sintered glass, sintered metal, porous rubber tube, porous metal tube, porous ceramic or stainless steel. The spray can be several degrees (ie, porosities) to provide a Vcocpjq gurgihkeq fg “dqnjc”

[0050] Q Vgtoq “dqecF’ glqw “ecdg>c fg ejwxgitq” eqortggnfg w device that divides a liquid flow into multiple liquid jets. In a particular embodiment, the mouthpiece is a perforated tube with pores down.

[0051] Eqoq tgfgtifq cswi, “gurwoc” fi woc ocuuc fg dqnjcu of gas in a matrix of liquid films. The volumetric gas fraction in the foam is preferably greater than 70%.

[0052] C "eqnxgtu«q" fg wo uwduVtcVq fi c rtqrqt>«q fg wo uwduVtcVq reacted during the reaction for the total amount of a substrate supplied to the reactor.

[0053] Q Vgtoq "tgVgn>«q fg iáu" inenwi c ftc>«q fg iáu xqnwofiVtiec in a two-phase liquid-gas mixture.

[0054] Q Vgtoq "Vtcnufgtêneic fg ocuuc" wVüizcfq cswi predominantly means the transfer of gaseous substrates to the liquid medium in which the micro-organism resides.

[0055] Qu Vgtoqu "gfieiêneic fg Vtcnufgtêneic fg ocuuc". “gfieiêneic fg Vtcnufgtêneic fg ocuuc xqnwofiVtiec” g uioinctgu. it is the rate of dissolution of the gaseous substrate within the liquid medium per unit of time per unit of reactor volume.

[0056] Qu Vgtoqu "cwognVcnfq c gfieiêneic". "gfieiêneic cwognVcfc" and the like, when used in connection with a mass transfer process, refer to the highest rate of dissolution of the gaseous substrate in the liquid medium.

[0057] Unless the context requires otherwise, the similar phrases "fgtognVcnfq", "rtqeguuq fg fgtognVc>«q" qw "tgc>«q fg fgtognVc>«q" g, as used herein, are intended to encompass the phase of growth and the biosynthesis phase of the product of the process.

[0058] Efficient fermentation of gaseous substrates to produce the products requires control of the amount of substrate transferred within a fermentation broth to ensure high rates of production of desired products and the prevention of inhibition. In addition, in order to maximize carbon capture, the amount of a substrate transferred within the fermentation broth, so that it can be converted by one or more microorganisms, must be kept at a high level. Also, in order to maintain overall efficiency, the substrate must be transferred into the solution so that power input through the system is minimized.

[0059] According to the invention, there is provided a system for an improved fermentation of a gaseous substrate by introducing a secondary loop to a forced circulation external loop reactor. The reactor comprises a primary cycle through which fermentation broth comprising a gaseous substrate is circulated through a riser segment and a falloff section by a cycle pump. Downstream of the cycle pump a portion of the fermentation broth is withdrawn from the descent section and is directed to the top of the reactor through a secondary cycle. In particular embodiments, the portion of fermentation broth removed from the primary cycle is sprayed from the secondary cycle through a nozzle.

[0060] The primary rate limiting step in gas fermentation is gas-to-liquid mass transfer. Known means of increasing mass transfer are by stirring a mixture of gas and liquid, such as mechanical stirring of the broth. However, these known methods to increase mass transfer require a large input force, which becomes inefficient and/or uneconomical as the scale increases.

[0061] The reactor of the present invention is configured to significantly improve the mass transfer from a gas phase to a liquid phase. In particular embodiments, a portion of the liquid flow is withdrawn from the cycle pump discharge in the descending section and, therefore, the volumetric liquid flow rate in the ascent section is less than that in the descending section. In certain embodiments, the removal of the fermentation broth portion from the descending section results in increased gas retention and mass transfer in the riser section of the reactor.

[0062] In a particular embodiment of an apparatus of the invention, the reactor consists of a rise section and a fall section. The rise and fall are connected by two horizontal sections at each end to form a primary loop, and the liquid/gas flow through is directed through the primary loop at least partially by a pump at the bottom of the descent. In particular embodiments, the gas is introduced into the system through an appropriate type of sprayer. In particular embodiments, a secondary loop line connects to the bottom of the descent and the top of the reactor to form a secondary loop. In particular embodiments, the secondary loop line is connected downstream of the descent of the primary loop pump, but before the ascent. In particular embodiments, the secondary cycle line draws a stream of liquid from the cycle pump discharge by a secondary pump. In particular embodiments, a liquid stream is passed to the top of the reactor through a secondary loop line, whereby liquid is sprayed into the headspace of the reactor through at least one nozzle. In certain embodiments, the at least one nozzle is a shower head.

[0063] In embodiments of the invention, the system has application in the fermentation of gaseous substrates for one or more products, said products including acids, alcohols and diols. In particular, ethanol, acetic acid and 2,3-butanediol are produced by fermentation of a gaseous substrate comprising CO. Alternative products include butanol, lactate, succinate, methyl ethyl ketone (MEK), propanediol, 2-propanol, isopropanol, acetoin, iso-butanol, citramalate, butadiene, polylactic acid, isobutylene, 3-hydroxy propionate (3HP), acetone, fatty acids and mixtures thereof.

[0064] Typically, the head space of the reactor riser section comprises a layer of foam resulting from the rising gas and agitation of the broth. The present invention allows the fermentation broth used in the reactor fermentation process to be sprayed onto the foam layer, where the spray has the effect of breaking up large gas bubbles in the foam. Large gas bubbles rise with greater velocity through the liquid and therefore have a shorter rise time residence with less mass transfer of the contained gas. By breaking up the large gas bubbles, the smaller bubbles are drawn back into the descending section of the reactor, which further provides the opportunity for mass transfer. In another embodiment, the shower is sprayed onto the foam layer in the headspace to effectively break the foam so that it does not build up and block the pipelines downstream of the reactor.

[0065] In another modality, the shower transforms the foam layer into a gas-liquid contact countercurrent in which the liquid flows downwards and the gas flows upwards. The mass transfer efficiency in this countercurrent flow itself is high due to the countercurrent action and the high gas content. Although the concentration of the gaseous substrate in the gaseous phase may be poor, this part of the reactor will contribute a significant amount to substrate uptake. When there are fluctuations in the gas supply, the gas foam height can be adjusted accordingly to maintain a stable production rate.

[0066] The fermentation can be conducted in any acceptable bioreactor, such as an immobilized cell reactor, a gas lift reactor, a bubble column reactor (BCR), a membrane reactor, such as a Hollow Fiber Membrane Bioreactor (HFM BR) or a drip bed reactor (TBR). Also, in some embodiments of the invention, the bioreactor may comprise a first growth reactor in which microorganisms are cultured, and one or more production fermentation reactors configured in series or in parallel, to which the reactor fermentation broth of growth can be fed and in which the majority of the fermentation product (eg ethanol and acetate) can be produced. The bioreactor of the present invention is adapted to receive substrate containing CO and/or H2, or a CO2 and/or H2.

[0067] In particular modes, the gas inlet is located at the bottom of the reactor riser section. The inventors have identified that an excess of CO in the area close to the gas inlet (ie, the bottom of the ascent) results in inhibition of the microorganism. However, this problem is surprisingly overcome by the present invention. In particular embodiments, the gas inlet in the headspace of the reactor riser section comprises a lower CO content than the fresh inlet gas at the bottom of the riser. When the entrained gas is eventually recycled through the descent to return to the bottom of the ascent, the entrained gas mixes with the fresh inlet gas and reduces the concentration of dissolved CO at the bottom of the ascent, effectively reducing the chance of substrate inhibition and improving overall CO conversion. The same problem can also be solved by splitting the fed gas into more than one stream and injecting them at multiple sites in the rise and fall of the reactor. The latter method, however, does not significantly improve CO conversion.

[0068] According to particular embodiments, the mass transfer rate from the gaseous substrate to the microbial culture can be controlled so that the microbial culture is supplied with the substrate at or for an optimal supply rate. In reactors, the mass transfer rate can be controlled by controlling the partial pressure of the gaseous substrate and/or by controlling the liquid flow rate or gas retention. In particular embodiments, mass transfer is controlled by controlling the rate at which the fermentation broth is pumped through both the primary and secondary reactor cycles.

[0069] In particular embodiments, fresh gas is introduced into the container by one or more gas inlet. Typically, high mass transfer can be achieved by introducing the gaseous substrate as fine bubbles. Those skilled in the art will appreciate means for introducing the gaseous substrate, such as sprinklers. In particular embodiments, gas is introduced into the container by fine-bubble diffusers or another type of fine-bubble generator.

[0070] Upon consideration of the present disclosure, those skilled in the art will appreciate the size and type of pumps required to circulate fermentation broth comprising one or more microorganisms around the primary and secondary cycles. It should be noted that the greater the retention of gas in the liquid, the lower the density of the liquid, so the pump needs to be configured to circulate liquids of varying densities according to the change in the composition of the gas/liquid suspension. By way of examples without limitation, one or more multistage pumps configured to pump the fermentation broth/gas suspension can be used to circulate a single liquid phase and increase the discharge pressure of a fluid. Using a rotary impeller, liquid enters the pump along an axis of rotation of the motor and accelerates the liquid radially outward through a diffusion chamber. Centrifuge pumps can also operate with smaller two-stage gas retention without cavitation (a known vulnerability of centrifugal pumps), maintaining an adequate liquid positive suction head. Those skilled in the art will appreciate that there are multi-stage pumping solutions for large-scale applications.

[0071] In alternative embodiments, the fermentation vessel descending section comprises a gate valve located upstream of the secondary cycle outlet. In this modality, fermentation broth can be withdrawn from the descent to the secondary cycle by restricting the flow of the primary cycle using the gate valve. By adjusting the gate valve opening, the cycle pump down pressure upstream of the gate valve can be regulated to provide a desired secondary cycle flow rate. In certain modalities, the descent pressure is monitored by a pressure gauge. This configuration eliminates the requirement for a secondary cycle pump.

[0072] In particular modalities, the secondary cycle is integrated with a cell recycling system. The cell recycling system provides a means to separate microorganisms that are returned to the reactor for further fermentation. A cell recycling module continuously attracts the permeated broth while retaining the cells. Those skilled in the art would understand that cell recycle members can include, but are not limited to, cell recycle membranes or disk stack centrifuge separators. In preferred embodiments, cells are retained in the fermentation broth using ultrafiltration. In certain embodiments, the driving force for the secondary cycle is derived from the cell recycling pump. In preferred embodiments, the cell recycling pump is much larger than the secondary cycle pumps described above. In a particular embodiment, fermentation broth is withdrawn downstream of the secondary cycle of the cell recycle module. In particular embodiments, the secondary cycle flow rate and pressure of the cell recycling system are regulated by at least one control valve upstream of the cell recycling module. In particular embodiments, the secondary cycle flow rate is regulated by two control valves upstream of the cell recycling module. The first control valve regulates the flow to the top of the reactor through the secondary loop line. The second control valve regulates the flow to a separate line that returns the fermentation broth to the descent. In certain embodiments, in order to increase the secondary cycle flow rate, the flow through the first control valve is increased and the flow through the second control valve is restricted. In order to decrease the secondary cycle flow rate, the flow through the first control valve is restricted and the flow through the second control valve is increased. So that cell recycling flow requirements are met, the two control valves are configured to maintain a constant flow rate through the cell recycling module.

[0073] The reactor of the present invention can additionally include a wide range of suitable gas/liquid contact modules that can provide effective mass transfer of a gaseous substrate needed to improve the efficiency of microbial fermentations. A contact module provides a unique geometric environment allowing the gas and liquid to completely mix along an established flow path, causing the entrained gas to dissolve into the liquid evenly. By way of example, these contact modules include, among others, a structured corrugated metal packaging matrix, random packaging, sieve plates and static mixers, all of which have a well known range of types and density and are widely commercially available. .

[0074] Various embodiments of the systems of the invention are described in the attached Figures.

[0075] Figure 1 is a schematic diagram of an embodiment of a looped loop reactor comprising a secondary loop. The reactor consists of a rise (2), in which the mixture of liquid and gas (3) concurrently flows upwards, and a descent (8), in which the liquid and gas concurrently flow downwards. The rise (2) and fall (8) are connected by two horizontal sections at each end and the two-phase flow is driven at least partially by a pump (9) at the bottom of the fall (8). Gas is introduced into the system through one or more appropriate types of sprayers (1). A portion of the gas is carried into the descent (8) by the flow of liquid in the gas-liquid separator (4), and this portion of the gas is referred to eqoq q "iáu circuVcfq" qw q "iáu tgekelcfq" cswko Q iáu p«q cttcuVcfq fgkzc q system through a control valve (7), after passing the upper space (6). Typically, there is a foam layer (5) of some height above the liquid level in the head space (6). It can be seen from this diagram that the mixture of liquid and gas flows from the rise (2) to the fall (8) and back forming a cycle (ie the primary cycle).

[0076] The secondary cycle circulates the fermentation broth (3) from the bottom of the descent (8) to the top of the reactor. Downstream of the primary cycle pump (9), but before the rise (2), a stream of liquid is withdrawn from the discharge of the cycle pump (9) by a secondary pump (11). The current is passed to the top of the reactor through a secondary loop line (12), whereby liquid is sprayed into the head space (6) through an appropriate spray nozzle or shower head (10). The liquid is sprayed onto the surface of the foam layer (5) at a speed of about 0.5 m/s to about 5 m/s so as to break the foam. The secondary cycle liquid flow rate is measured and monitored by a flow meter (13).

[0077] Figure 2 shows a schematic diagram of an alternative embodiment of the looped loop reactor comprising a gate valve (14). Other reactor components are removed from the figure for clarity. By adjusting the gate valve opening, the down pressure of the cycle pump, but upstream of the gate valve, can be regulated to generate a secondary cycle flow rate. Pressure is monitored by a pressure gauge (15). This configuration eliminates the requirement for a secondary cycle pump.

[0078] Figure 3 shows a schematic diagram of an alternative embodiment of the looped loop reactor comprising an integrated cell recycling system. Other reactor components are removed from the figure for clarity. In this modality, the secondary cycle is withdrawn downstream of the cell recycling module (19), where the driving force for the secondary cycle comes from a cell recycling pump (16). In preferred embodiments, the cell recycling pump is much larger than the secondary cycle pump described above. In particular embodiments, the cell recycle module separates cells from the permeate using ultrafiltration or other separation means such as membrane. Only a portion of the fermentation broth supplied to the cell recycling module is passed on top of the reactor and therefore the secondary cycle flow rate and the pressure of the cell recycling system are regulated by two control valves (17, 18 ) downstream of the cell recycling module (19). The first control valve (17) regulates the flow to the top of the reactor through the secondary loop line. The second control valve (18) regulates the flow to a separate line that returns the fermentation broth to the descent. In certain embodiments, in order to increase the secondary cycle flow rate, the flow through the first control valve (17) is increased and the flow through the second control valve (18) is restricted. In order to decrease the flow rate of the secondary cycle, the flow through the first control valve (17) is restricted and the flow through the second control valve (18) is increased. In order that the requirements for cell recycling flow are met, the two control valves (17, 18) are configured to maintain a constant flow rate through the cell recycling module (19).

[0079] It should be noted that various changes and modifications to the present preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the invention and without diminishing its attendant advantages. It is, therefore, understood that such changes and modifications may be included within the scope of the invention.

Fermentation

[0080] Processes for the production of ethanol and other alcohols from gaseous substrates (such as those described in the fundamentals section above) are known. Exemplary processes include those described, for example, in WO 2007/117157 and WO 2008/115080, as well as US Patents 6,340,581, 6,136,577, 5,593,886, 5,807,722 and 5,821,111, each of which is incorporated herein by reference.

[0081] A number of anaerobic bacteria are known to be capable of conducting fermentation from CO to alcohols, including n-butanol and ethanol, acetic acid and are suitable for use in the processes of the present invention. Examples of such bacteria which are suitable for use in the invention include those of the genus Clostridium, such as strains of Clostridium ljungdahlii, including those described in WO 00/68407, EP 117309, US Patents 5,173,429, 5,593,886 and 6,368,819 , WO 98/00558 and WO 02/08438, Clostridium carboxydivorans (Liou et al., International Journal of Systematic and Evolutionary Microbiology 33: pp 2085-2091) and Clostridium autoethanogenum (Abrini et al., Archives of Microbiology 161: pp 345- 351). Other suitable bacteria include those of the genus Moorella, including Moorella sp HUC22-1 (Sakai et al., Biotechnology Letters 29: pp 16071612), and those of the genus Carboxydothermus (Svetlichny, VA, et al. (1991), Systematic and Applied Microbiology 14: 254-260). The disclosures of each of these publications are incorporated herein by reference. In addition, other anaerobic carboxydotrophic bacteria can be used in the processes of the invention by a person skilled in the art. It will also be appreciated in considering the present disclosure that a mixed culture of two or more bacteria can be used in the processes of the present invention.

[0082] Cultivation of the bacteria used in a method of the invention may be conducted using any number of processes known in the art for the cultivation and fermentation of substrates using bacteria cpcgt„dkecUo Vfiepkecu gzgornctgu u«q fomgekfcu pc ug>«q "Gzgornou" bellow. By way of another example, these processes generally described in the articles below using gaseous substrates for fermentation can be used: (i) K. T. Klasson, et al. (1991). Bioreactors for synthesis gas fermentations resources. Conservation and Recycling, 5; 145-165; (ii) K.T. Klasson, et al. (1991). Bioreactor design for synthesis gas fermentations. Fuel. 70, 605-614; (iii) K.T. Klasson, et al. (1992). Bioconversion of synthesis gas into liquid or gaseous fuels. Enzyme and Microbial Technology. 14; 602-608; (iv) J.L. Vega, et al. (1989). Study of Gaseous Substrate Fermentation: Carbon Monoxide Conversion to Acetate. 2. Continuous Culture. Biotech. Bioeng. 34.6.785-793; (vi) J.L. Vega, et al. (1989). Study of gaseous substrate fermentations: Carbon monoxide conversion to acetate. 1. Batch culture. Biotechnology and Bioengineering. 34.6,774-784; (vii) J.L. Vega, et al. (nineteen ninety). Design of Bioreactors for Coal Synthesis Gas Fermentations. Resources, Conservation and Recycling. 3.149-160; all of which are incorporated herein by reference.

[0083] In one embodiment, the micro-organism is selected from the group consisting of Clostridia carboxidotrophic comprising Clostridium autoethanogenum, Clostridium ljungdahlii, Clostridium ragsdalei, Clostridium carboxidivorans, Clostridium drakei, Clostridium scatologenes, Clostridium acetictridium, acetictridium magnum In another embodiment, the microorganism is from a carboxydotrophic Clostridia group comprising the species C. autoethanogenum, C. ljungdahlii and C. ragsdalei and related isolates. These include, among others, C. autoethanogenum JAI-1T (DSM10061) strains (Abrini, Naveau, & Nyns, 1994), C. autoethanogenum LBS1560 (DSM19630) (WO/2009/064200), C. autoethanogenum LBS1561(DSM23693), C. Ijungdahlii PETCT (DSM13528 = ATCC 55383) (Tanner, Miller, & Yang, 1993), C. Ijungdahlii ERI-2 (ATCC 55380) (US Patent 5,593,886), C. Ijungdahlii C-01 (ATCC 55988) ( US Patent 6,368,819), C. Ijungdahlii O-52 (ATCC 55989) (US Patent 6,368,819), C. ragsdalei P11T (ATCC BAA-844+ *YQ 422:124:277+. kuqncfqu tgncekqpcfqu Vcku eqoq "C . coskatii” *WU4233244;;69+ g “Enqsttkfkwo up.” (Tyurin & Kiriukhin, 2012), or mutated strains such as C. ljungdahlii OTA-1 (Tirado-Acevedo O. Production of Bioethanol from Synthesis Gas Using Clostridium ljungdahlii. PhD thesis, North Carolina State University, 2010) These strains form a subcluster within Clostridial rRNA cluster I, and their 16S rRNA genes are more than 99% identical with a similar low GC content of about 30%. experiment DNA-DNA reassociation and DNA printing showed that these strains belong to distinct species (WO 2008/028055).

[0084] All species from the groups referenced above have a similar morphology and size (log cell growth is between 0.5-0.7 x 3-7 μo+. u«q oesophilic (optimal growth temperature between 30-37°C) °C) and strictly anaerobic (Abrini et al., 1994; Tanner et al., 1993) (WO 2008/028055) Furthermore, they all share the same major phylogenetic traits, such as the same pH range (pH 4 -7.5, with an optimal initial pH of 5.5-6), strong autotrophic growth in CO-containing gases with similar growth rates and a similar metabolic profile with ethanol and acetic acid as the main fermentation end-product, and small amounts of 2,3-butanediol and lactic acid formed under certain conditions (Abrini et al., 1994; Kopke et al., 2011; Tanner et al., 1993) (WO 2008/028055) Indole production was observed with all three species as well. However the species differ in substrate utilization of various sugars (eg, rhamnose, a rabinose), acids (eg gluconate, citrate), amino acids (eg arginine, histidine), or other substrates (eg betaine, butanol). Also, some of the species were found to be autotrophic for certain vitamins (eg, thiamine, biotin) while others were not. The organization and number of genes in the Wood-Ljungdahl pathway responsible for gas consumption was found to be the same in all species, despite differences in nucleic and amino acid sequences (Kopke et al., 2011). Also the reduction of carboxylic acids to their corresponding alcohols has been shown in a range of these organisms (Perez, Richter, Loftus, & Angenent, 2012). These traits are therefore not specific to an organism such as C. autoethanogenum or C. ljungdahlii, but rather general traits for Clostridia carboxidotrophic, an ethanol synthesizer and it can be anticipated that the working mechanism is similar in these strains, although they may there are differences in performance (Perez et al., 2012).

[0085] An exemplary microorganism suitable for use in the present invention is Clostridium autoethanogenum. In one embodiment, Clostridium autoethanogenum is a Clostridium autoethanogenum having the strain identification characteristics deposited at the German Resource Center for Biological Material (DSMZ) under deposit identification number 19630. In another embodiment, Clostridium autoethanogenum is a Clostridium autoethanogenum having the DSMZ identification characteristics of warehouse number DSM 10061.

[0086] The fermentation can be conducted in any suitable bioreactor. In some embodiments of the invention, the bioreactor may comprise a first growth reactor in which microorganisms are cultured, and one or more subsequent fermentation reactors configured in parallel or in series, to which the fermentation broth from the growth reactor is fed and where the majority of the fermentation product (eg ethanol and acetate) is produced.

[0087] According to various embodiments of the invention, the carbon source for the fermentation reaction is a gaseous substrate containing CO. The gaseous substrate can be a CO-containing waste gas obtained as a by-product of an industrial process, or from some other source such as automobile exhaust. In certain embodiments, the industrial process is selected from the group consisting of manufacturing of ferrous metal products such as is conducted in a steel mill, manufacturing of non-ferrous products, petroleum refining processes, coal gasification, energy production electrical, black carbon production, ammonia production, methanol production and coca manufacturing. In these modalities, the gas containing CO can be captured from an industrial process before it is emitted into the atmosphere, using any convenient method. Alternatively, the gaseous substrate is a source of reformed gas, including natural gas, shale gas, associated petroleum gas and biogas. Depending on the gaseous composition of the CO-containing substrate, it may also be desirable to treat it to remove any unwanted impurities, such as dust particles, before introducing it to the fermentation. For example, the gaseous substrate can be filtered or rubbed using known methods.

[0088] The CO-containing substrate will ideally contain a significant proportion of CO, such as at least 5% to about 100% CO by volume, or 20% to 95% CO by volume, or 40% to 95% % CO by volume, or 60% to 90% CO by volume or 70% to 90% CO by volume. Gaseous substrates having lower concentrations of CO, such as 6%, may also be suitable, particularly when H2 and CO2 are also present.

[0089] Although it is not necessary for the gaseous substrate to contain any hydrogen, the presence of hydrogen will generally not be detrimental to product formation according to the methods of the invention. However, in certain embodiments of the invention, the gaseous substrate is substantially free of hydrogen (less than 1%). The gaseous substrate may also contain some CO2 such as about 1% to about 30% by volume, or such as about 5% to about 10% CO2.

[0090] As noted earlier, the presence of hydrogen in the substrate stream can lead to an improvement in overall carbon capture efficiency and/or ethanol productivity. For example, WO0208438 describes the production of ethanol using gas streams of various compositions.

[0091] Thus, it may be necessary to change the composition of the substrate stream in order to improve alcohol production and/or general carbon capture. Additionally or alternatively, the composition can be altered (ie adjusted levels of CO, CO2 and/or H2) to optimize the efficiency of the fermentation reaction and ultimately improve alcohol production and/or overall carbon capture.

[0092] In some embodiments, the gaseous substrate containing CO may be from the gasification source of organic matter such as methane, ethane, propane, coal, natural gas, crude oil, low residual values of refinery oil (including petroleum coca or petcoca), municipal solid waste or biomass. Biomass includes by-products obtained during the extraction and processing of foodstuffs, such as sugar from sugar cane, or starch from corn or grains, or residue from non-food biomass generated by the forest industry. Any of these carbonaceous materials can be gasified, that is, partially combusted with oxygen, to produce synthetic gas (singers comprising significant amounts of H2 and CO). Gasification processes typically produce a synthetic gas with a molar ratio of H2 to CO of about 0.4:1 to 1.2:1, along with smaller amounts of CO2, H2S, methane and other inert substances. The proportion of gas produced can be varied by means known in the art and are described in detail in WO200701616. However, by way of example, the following gaseous conditions can be changed to adjust the CO:H2 product ratio: raw material composition (particularly C:H ratio), operating pressure, temperature profile (influencing the extinction of the mixture of products) and oxidant employed (air, oxygen-enriched air, pure O2 or steam; where steam tends to result in higher proportions of CO:H2). Thus, the gasifier operating conditions can be adjusted to provide a substrate stream with a desired composition for fermentation or mixing with one or more other streams to provide an optimized or desired composition for increasing alcohol productivity and/or capturing alcohol. general carbon in a fermentation process.

[0093] In other embodiments, the substrate comprising CO can be derived from hydrocarbon vapor reforming. Hydrocarbons such as natural gas hydrocarbons can be reformed at high temperature to generate CO and H2 as follows:

[0094] By way of example, methane steam reforming involves reacting the steam with methane to produce CO and H2 at elevated temperature (700-1100°C) in the presence of a nickel catalyst. The resulting stream (comprising 1 mole of CO and 3 moles of H2 for every mole of CH4 converted) can be passed directly to the fermentor or mixed with a substrate stream from another source to increase ethanol productivity and/or carbon capture general in a fermentation process. Alcohols such as methane can also be reformed to produce CO2 and H2 that can be used in a similar way.

[0095] In another embodiment, the substrate comprising CO is derived from steel manufacturing process. In a steelmaking process, iron ore is crushed and pulverized, subjected to pre-treatments such as sintering or pelletizing, and then passed to a furnace (BF) where it is melted. In a smelting process, coca serves as the carbon source, which works as a reducing agent to reduce iron ore. Coca acts as the heating source to heat and melt the materials. The hot metal is decarburized in a basic oxygen furnace (BOF) by injecting a high-speed jet of pure oxygen against the surface of the hot metal. Oxygen reacts directly with carbon in the hot metal to produce carbon monoxide (CO). Therefore, a gas stream with a high CO content is released from the BOF. In accordance with certain embodiments of the invention, this stream is used to fuel one or more fermentation reactions. However, as would be apparent to one skilled in the art, CO can be produced elsewhere within the steelmaking process, and according to various embodiments of the invention, such alternative sources can be used instead of or in combination with gases of exhaustion by BOF. Depending on the source (ie the particular stage within the steelmaking process), the CO content of the exhaust gases in this way can vary. Also, there may be periods when there is a break in one or more of these chains, particularly in batch processing plants.

[0096] Typically, streams released by steel mill decarburization process comprise high concentration of CO and low concentrations of H2. While such streams can be directly passed to the bioreactor with little or no other treatment, it may be desirable to optimize the composition of the substrate stream in order to achieve greater alcohol production efficiency and/or overall carbon capture. For example, the concentration of H2 in the substrate stream can be increased before the current is passed through the bioreactor.

[0097] According to particular embodiments of the invention, streams from two or more sources can be combined and/or mixed to produce a desired and/or optimized substrate stream. For example, a stream comprising a high concentration of CO, such as that released by a steel mill converter, can be combined with a stream comprising high concentrations of H2, such as the off-gas of a steel mill coca oven. steel.

[0098] Alternatively or additionally, an intermittent stream comprising CO, such as a stream released from a converter, may be combined with and/or mixed with a direct current substantially comprising CO and optionally H2, such as the singas produced in a process of gasification as described above. In certain embodiments, this would maintain the provision of a substantially continuous substrate stream to the bioreactor. In a particular embodiment, the current produced by a gasifier can be increased and/or decreased in accordance with the intermittent production of CO from an industrial source so as to maintain a continuous substrate current of substantially a desirable or optimized composition. In another embodiment, the gassing conditions can be changed as described above in order to increase or decrease the CO:H2 ratio, in accordance with the intermittent production of CO from an industrial source, so as to maintain a substantially continuous substrate current. with a desirable or optimized composition of CO and H2.

[0099] Typically, the substrate stream used in the invention will be gaseous; however, the invention is not limited to this. For example, carbon monoxide can be supplied to a bioreactor in a liquid. For example, the liquid can be saturated with a gas containing carbon monoxide and then the liquid added to the bioreactor. This can be achieved using a standard methodology. As an example, a microbubble dispersion generator (Hensirisak et al., Scale-up of microbubble dispersion generator for aerobic fermentation; Applied Biochemistry and Biotechnology Volume 101, Number 3, October, 2002) could be used for this purpose.

[00100] It will be appreciated that for the growth of bacteria and the fermentation of CO to ethanol to occur, in addition to the gaseous substrate containing CO, a necessary liquid nutrient medium will be fed to the bioreactor. A nutrient medium will contain enough vitamins and minerals to allow the micro-organism used to grow. Suitable anaerobic media for the fermentation of ethanol using CO as the sole carbon source are known in the art. For example, suitable media are described in US Patents 5,173,429 and 5,593,886 and WO 02/08438, YQ42291337379 and YQ422:13372:2. reherifos cekoCo Qu “Gzeornos” cswk provide other exemplary means.

[00101] The fermentation should desirably be conducted under conditions appropriate for the desired fermentation to take place (eg CO to alcohol). Reaction conditions that should be considered include pressure, temperatures, gas flow rate, liquid flow rate, medium pH, medium redox potential, agitation rate (if using a continuous stirred tank reactor), level of inoculum, maximum gaseous substrate concentrations to ensure that liquid phase CO does not become limiting, and maximum product concentrations to avoid product inhibition.

[00102] The optimal reaction conditions will partly depend on the particular micro-organism used. However, in general, it may be preferable that the fermentation be carried out at a pressure greater than ambient pressure. Operating at increased pressures allows for a significant increase in the transfer rate of CO from the gas phase to the liquid phase where it can be used by the microorganism as a carbon source for ethanol production. This in turn means that retention time (defined as the net volume in the bioreactor divided by the inlet gas flow rate) can be reduced when bioreactors are kept at elevated pressure greater than atmospheric pressure.

[00103] Further, because a given conversion rate of CO to ethanol is in part a function of the substrate retention time, and achieving a desired retention time in turn dictates the required volume of a bioreactor, the use of systems Pressurized can greatly reduce the required volume of a bioreactor, and hence the capital cost of fermentation equipment. According to the examples given in US Patent no. 5,593,886, the reactor volume can be reduced in a linear proportion to increase the operating pressure in the reactor, ie bioreactors operated at 10 atmospheres of pressure need only be one-tenth the volume of those operated at 1 atmosphere of pressure.

[00104] The benefits of conducting a gas fermentation for ethanol at elevated pressures have also been described elsewhere. For example, WO 02/08438 describes gas fermentations for ethanol carried out at pressures of 30 psig and 75 psig, generating ethanol productivities of 150 g/l/day and 369 g/l/day respectively. However, examples of fermentations using similar medium and atmospheric pressure inlet gas compositions have been found to produce between 10 and 20 times less ethanol per liter per day.

[00105] It is also desirable that the rate of introduction of the gaseous substrate containing CO is such to ensure that the concentration of CO in the liquid phase does not become limiting. This is because a consequence of limited CO conditions may be that the ethanol product is consumed by the crop.Product Recovery

[00106] The products of the fermentation reaction can be recovered using known methods. Exemplary methods include those described in WO2007/117157, WO2008/115080 and US Patents 6,340,581, 6,136,577, 5,593,886, 5,807,722 and 5,821,111. However, briefly and by way of example only, ethanol can be recovered from the fermentation broth by methods such as fractional distillation or evaporation, and extractive fermentation.

[00107] Distilling ethanol from the fermentation broth yields an azeotropic mixture of ethanol and water (ie 95% ethanol and 5% water). Anhydrous ethanol can subsequently be obtained through the use of molecular sieve ethanol dehydration technology, which is also known in the art.

[00108] Extractive fermentation procedures involve the use of a water-miscible solvent that poses a low risk of toxicity to the fermentation organism, to recover the ethanol from the diluted fermentation broth. For example, oleyl alcohol is a solvent that can be used in this type of extraction process. In this process, oleyl alcohol is continuously introduced into a fermenter, over which this solvent rises forming a layer on top of the fermenter which is continuously extracted and fed through a centrifuge. Water and cells are then quickly separated from the oleyl alcohol and returned to the fermentor while the ethanol-laden solvent is fed into a flash vaporizer unit. Most of the ethanol is vaporized and condensed while non-volatile oil is recovered for reuse in fermentation.

[00109] Acetate can also be recovered from the fermentation broth using methods known in the art. For example, an absorption system involving an activated carbon filter can be used. In this case, microbial cells are typically first removed from the fermentation broth using a suitable separation method. Numerous cell-free fermentation broth generation filtration-based methods for product recovery are known in the art. The cell-free ethanol - and acetate - containing the permeate is then passed through a column containing activated carbon to absorb the acetate. Acetate in the acid form (acetic acid) rather than the salt form (acetate) is more readily absorbed by activated charcoal. It is, therefore, preferred that the pH of the fermentation broth be reduced to less than about 3 before it is passed through the activated carbon column, to convert most of the acetate to the acetic acid form.

[00110] Fermentation reaction products (eg ethanol and acetate) can be recovered from the fermentation broth by continuously removing a portion of the broth from the fermentation bioreactor, separating microbial cells from the broth (conveniently by filtration), and recovering one or more broth products simultaneously or sequentially. Ethanol can conveniently be recovered by distillation, and acetate can be recovered by absorption onto activated carbon, using the methods described above. Cell-free permeate remaining after ethanol and acetate have been removed can also be returned to the fermentation bioreactor. Additional nutrients (such as B vitamins) can be added to the cell-free permeate to replenish the nutrient medium before being returned to the bioreactor. Also, if the pH of the broth has been adjusted as described above to improve the absorption of acetic acid by activated carbon, the pH must be readjusted to a pH similar to that of the broth in the fermentation bioreactor, before being returned to the bioreactor.Off- Industrial Gas as a Source for Fermentation

[00111] According to other aspects of the invention, industrial waste gases are used in a fermentation reaction with no or only minimal friction or additional pretreatment steps being used to prepare the appropriate gases from the same.

[00112] Waste gases can result from any number of industrial processes. The invention has particular applicability to support the production of ethanol from gaseous substrate such as high volume industrial flue gases containing CO. Examples of gases produced during the manufacture of ferrous metal products, manufacture of non-ferrous products, refinery processes, oil refining processes, coal gasification, biomass gasification, electricity production, black carbon production, ammonia production , methanol production and coca manufacturing. In certain embodiments, the CO-containing substrate is derived from the gasification of biomass or municipal solid waste. In a particular embodiment of the invention, waste gases are generated during a process for producing steel. For example, those skilled in the art will appreciate that waste gases produced during various stages of the steelmaking process have high concentrations of CO and/or CO2. In particular, the tail gas produced during the decarburization of steel in various steel manufacturing methods, such as in an oxygen converter (eg BOF or KOBM), has a high CO content and a low O2 content making it o a suitable substrate for anaerobic carboxydotrophic fermentation.

[00113] The waste gases produced during the carburization of steel are optionally passed through water to remove particulate material before passing to a waste pile or combustion to direct the waste gas into the atmosphere. Typically, gases are directed into a waste pile with one or more fans.

[00114] In particular embodiments of the invention, at least a portion of the residual gas during the decarburization of steel is diverted to a fermentation system by any suitable conduction means. By way of example, piping or other transfer means can be connected to the waste gas stack of a steel mill to divert at least a portion of the waste gas to a fermentation system. Again, one or more fans can be used to divert at least a portion of the waste gas in a fermentation system. In particular embodiments of the invention, the driving means are adapted to supply at least a portion of the waste gas produced during the decarburization of steel to a fermentation system. The control and means for feeding gases into a bioreactor will be readily apparent to those skilled in the art to which the invention is concerned.

[00115] While steel mills can be adapted to substantially continuously produce steel and subsequently tail gas, particular aspects of the process can be intermittent. Typically, steel decarburization is a bath process lasting from long minutes to long hours. In this way, the conduction means can be adapted to divert at least a portion of the tail gas, such as the gas produced during the decarburization of steel, to the system for determining whether it is determined that the tail gas has a desirable composition.

[00116] The pH content of the bioreactor used in the fermentation process can be adjusted as required. The appropriate pH will be dependent on the conditions required for a particular fermentation reaction having regard to the nutrient medium and microorganisms used, as will be appreciated by those skilled in the art to which the invention pertains. In a preferred embodiment, in the fermentation of a CO-containing gaseous substrate using Clostridium autoethanogenum, the pH can be adjusted to approximately 5.5 to 6.5, more preferably to approximately 5.5. Other examples include pH 5.5 to 6.5 using Moorella thermoacetica for acetic acid production, pH 4.5 to 6.5 using Clostridium acetobutylicum for butanol production, and pH 7 using Carboxydothermus hygrogenaformans for hydrogen production. Those skilled in the art will be aware of suitable means to maintain the bioreactor at the required pH. However, by way of example, aqueous bases such as NaOH and aqueous acids such as H2SO4 can be used to raise and lower the pH of the fermentation medium and maintain the desired pH.

[00117] An additional benefit of the invention is that, due to having no or only minimal friction and/or other treatment processes performed on the waste gases prior to their use in a fermentation reaction, the gases will contain additional material resulting from the industrial process , whose additional material can be used, at least in part, as raw material for the fermentation reaction.

[00118] Bacteria: Clostridium autoethanogenum used is deposited at the German Resource Center for Biological Material (DSMZ) and assigned accession numbers DSMZ 19630.

[00119] Fermentation: The medium was prepared according to the composition described in Tables 1-3 to a volume of 1.5 l and 1.5 ml of resazurin was added. The solution was heated and stirred while degassing with N2. A drop of ANa2S was started at a rate of 0.1ml/hr and the bioreactor temperature adjusted to 37°C. The pH was adjusted to 5.0 with NH4OH and chromium was added to adjust the ORP to -200 mV. The bioreactor was then supplied with RMG (43% CO, 20% CO2, 2.5% H2 and 33% N2).Experiment 1: Effect of secondary cycle on liquid flow rate, gas retention and conversion of CO

[00120] The reactor comprised a rise with a diameter of 0.254 m and a descent with a diameter of 0.138 m. The reactor comprised a secondary cycle of 0.043m in diameter, withdrawing the juice at the top of the descent and circulating the juice using a mechanical pump to the top of the rise, in which the juice entered the upper space of the reactor through a shower head. The height of the reactor was 6 m. The reactor was tested during continuous fermentation of Clostridium autoethanogenum.

[00121] During the test, the liquid flow rate on the descent, QL,0 was 30 mVhr and the liquid flow rate in the second cycle QL,2 was 5.5 mVhr. By 20/02, the secondary cycle was turned off and an immediate decrease in hold down from 11% to 5% was observed, as shown in Figure 4. Cycle pump speed was increased to 30% to 50% during this period but it can be seen that this did not effectively improve hill retention due to the two competing effects of cycle pump speed on hill retention. On 8/20, the secondary cycle was reactivated and climb retention was improved immediately, even at a reduced cycle pump speed.

[00122] The effect of the second cycle on CO conversion during the same test period is shown in Figure 5. An immediate drop in CO conversion was observed after the secondary cycle was turned off, due to the decrease in hold up and therefore , a decrease in mass transfer area. This situation was slightly alleviated by continuously increasing the cycle pump, which increased descent hold. However, this approach was much less effective than reactivating the secondary cycle on Day 20/8.

[00123] The effect of the secondary cycle on hold up rise at different gas inlet flow rates was also investigated in a smaller reactor, with an upstream diameter of 3 inches and a height of 1.1 m. The separator of this smaller reactor had a diameter of 6 inches and an effective height of 270 mm. The drop diameter was 1.5 inches and the secondary loop diameter was 0.5 inches. The results in Figure 6 show that with the secondary cycle, ascent retention is significantly increased, especially at lower surface gas flow rates. There appears to be an upper limit of lift retention around 15%, which is related to changes in the flow regime in such a smaller reactor. However, a positive retention effect of the secondary cycle persists.Experiment 2: Effect of the secondary cycle on large-scale gas retention and CO conversion

[00124] Similar hydrodynamic experiments investigating the effect of the secondary cycle were carried out in reactors larger than 10 meters high, with 1 meter in diameter in the ascent and 0.5 meter in diameter in the descent. The secondary loop diameter was 2 inches. As shown in Figures 7 and 8, the results were similar. It can be seen from Figure 7 that both rise and fall hold increased linearly with an increase in secondary cycle pump speed, where mass transfer should improve accordingly. Figure 8 shows the effect of the secondary cycle on converting CO from another test into a reactor of the same size.

General

[00125] The embodiments of the invention are described by way of example. However, it should be appreciated that particular steps or stages needed in one sport may not be needed in others. Conversely, steps or stages included in the description of a particular embodiment may optionally be advantageously used in embodiments in which they are not specifically mentioned.

[00126] While the invention is broadly described with reference to any type of current that can be moved through or around the systems by any known transfer means, in certain embodiments, the substrate and/or exhaust streams are gaseous. Those skilled in the art will appreciate that particular stages can be coupled by suitable conduit means or the like, configurable to receive or pass currents through a system. A pump or compressor can be provided to facilitate the release of currents for particular stages. In addition, a compressor can be used to increase the pressure of gas supplied to one or more stages, eg the bioreactor. As discussed here above, the pressure of gases inside a bioreactor can affect the efficiency of the fermentation reaction carried out in it. Therefore, the pressure can be adjusted to improve fermentation efficiency. Suitable pressures for common reactions are known in the art.

[00127] In addition, the systems or processes of the invention may optionally include means to regulate and/or control other parameters to improve the overall efficiency of the process. One or more processes can be incorporated into the system to regulate and/or control particular process parameters. For example, particular embodiments may include means to monitor substrate composition and/or exhaust currents. In addition, particular embodiments may include means for controlling the release of a substrate stream to particular stages or elements within a particular system if the means of determining determines that the stream has a suitable composition for a particular stage. For example, in instances where the substrate gas stream contains low levels of CO or high levels of O2 that can be detrimental to a fermentation reaction, the substrate stream can be diverted away from the bioreactor. In particular embodiments of the invention, the system includes means to monitor and control the destination of a substrate stream and/or the flow rate so that a stream of a desired or suitable composition can be delivered to a particular stage.

[00128] In addition, it may be necessary to heat or cool components of the particular system or substrate stream prior to or during one or more stages in the process. In such instances, known means of heating or cooling can be used. For example, heat exchangers can be used to heat or cool substrate streams.

[00129] In addition, the system may include one or more pre/post treatment steps to improve the operation or efficiency of a particular stage. For example, the pre-treatment step may include means for removing particulate material and/or long chain hydrocarbons or tars from a gaseous substrate stream. Other pre/post operations that can be conducted include separating the desired products from particular stages, such as, for example, the bioreactor production stage (eg, removal of ethanol by distillation).

[00130] The invention has been described herein with reference to certain preferred embodiments, so as to enable the reader to practice the invention without undue experimentation. Those skilled in the art will appreciate that the invention can be practiced in a large number of variations and modifications. In addition, titles, headings, or the like are provided to add to the reader's understanding of this document, and should not be read as limiting the scope of the present invention. The full disclosures of all applications, patents and publications are cited herein and incorporated by reference.

[00131] More particularly, as will be appreciated by one skilled in the art, implementations of embodiments of the invention may include one or more additional elements. Only the elements necessary to understand the invention in its various aspects can be shown in a particular example or in the description. However, the scope of the invention is not limited to the described embodiments and included systems and/or methods including one or more additional steps and/or one or more substituted steps, and/or methods omitting one or more steps.

[00132] Reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that the prior art is common knowledge in the field of enterprise in any country.

[00133] Throughout this specification and any claim that follows, unless the context otherwise requires, the words "eqortggpfg". “eqortggpfgpfq” g ukoüctgu, fgxgo ugt kpVgtrtgVcfcu go wo inclusive sense as opposed to an exclusive sense, that is, in ugpuq fg “kpenwkpfq, gpVtg qwVtqu”

Claims (16)

1. Reactor system for the fermentation of a gaseous substrate, the system characterized in that it comprises: (a) a fermentation vessel comprising a riser section (2) in which a liquid fermentation broth (3) and the substrate gaseous are fluid concurrently upwards and a descending section (8) wherein the liquid fermentation broth (3) and the gaseous substrate are fluid concurrently downwards, said rising (2) and descending (8) sections connected by sections horizontal and configured so that the liquid fermentation broth (3) and the gaseous substrate are circulated, using pumping means, in a primary cycle from a point near the bottom of the descending section (8), through the rise (2) to an entry point at the top of the rise section (8); (b) a secondary loop comprising an exit location at a point near the bottom of the rise section (2), piping means connecting the exit at the bottom of the rise (2) for an entry at the top of the climb (2) and pumping means located between the exit point and the entry point so that the fermentation broth (3) and the gaseous substrate are circulated from the bottom of the descent (8) to the top of the riser section (2);( c) at least one gas inlet configured to direct the gaseous substrate within the riser section (2); and (d) at least one gas outlet, configured to allow gas to exit the riser section (2). 2. System according to claim 1, characterized in that the pumping means of (a) are located in the horizontal section connecting the bottom of the lowering section (8) to the bottom end of the rising section (2) and the output of the output of the secondary loop is located downstream of the pumping means. 3. System according to claim 1, characterized in that it further comprises at least one gate valve located below the pumping means of (a), the gate valve operated under conditions to regulate the pressure within the fermentation vessel and provide a desired secondary cycle flow rate. 4. System according to claim 1, characterized in that it further comprises at least one nozzle connected to the input of the secondary cycle at the top of the ascent section (2). 5. System according to claim 1, characterized in that the secondary cycle further comprises a cell recycling cycle comprising a cell recycling module (19) comprising a cell recycling pump (16), the cell recycling pump ( 16) acting as the pumping medium of (b). 6. Method for improving mass transfer from a gaseous substrate to a fermentation broth (3) in a fermentation vessel comprising a riser section (2) in which a liquid fermentation broth (3) and the gaseous substrate are fluid concurrently upwards and a descending section (8) in which the liquid fermentation broth (3) and the gaseous substrate are fluid concurrently downwards, the method characterized in that it comprises: (a) providing a gaseous substrate to the vessel a fermentation broth comprising a liquid nutrient medium and one or more microorganisms; (b) ferment the gaseous substrate to produce a fermentation broth (3) and at least one product; (c) circulate the fermentation broth (3) and the gaseous substrate through the rise section (2) and the fall section (8) of the fermentation vessel; and (d) passing at least a portion of the fermentation broth (3) from the bottom of the descending section (8) and circulating it to the top of the ascending section (2) through a secondary cycle, in which the broth from fermentation (3) enters the top of the climb section (2) through at least one nozzle. 7. Method for reducing foam in the head space (6) of a fermentation vessel comprising a riser section (2) in which the liquid fermentation broth (3) and the gaseous substrate are concurrently flowing upwards and a lowering section (8) wherein the liquid fermentation broth (3) and the gaseous substrate are concurrently flowed down, the method characterized in that it comprises: (a) providing a gaseous substrate to the fermentation vessel comprising a liquid nutrient medium and one or more microorganisms; (b) fermenting the gaseous substrate to produce a fermentation broth (3) and foam present in the head space (6) of the fermentation vessel of at least one product; (c) removing the fermentation broth (3) the descent section (8) of the fermentation vessel; and (d) circulating the fermentation broth (3) to the top of the riser section (2) through a secondary cycle, wherein the fermentation broth (3) enters the head space (6) through at least one nozzle ;wherein the fermentation broth (3) entering the head space (6) reduces the foam present inside the fermentation vessel. 8. Method according to claim 6 or 7, characterized in that the gaseous substrate is selected from the group consisting of CO, CO2, H2 and mixtures thereof. 9. Method according to claim 6 or 7, characterized in that the gaseous substrate is supplied to the bottom of the riser section (2) of the fermentation vessel. 10. Method according to claim 6 or 7, characterized in that the fermentation vessel comprises at least one pumping means to circulate the fermentation broth (3) through the rising section (2) and the falling section (8) from the fermentation vessel. 11. Method according to claim 6 or 7, characterized in that the secondary cycle comprises at least one secondary pumping means. 12. Method according to claim 6 or 7, characterized in that the secondary cycle further comprises a cell recycling module (19). 13. Method according to claim 6 or 7, characterized in that at least one nozzle comprises a shower head (10). 14. Method according to claim 6 or 7, characterized in that one or more microorganisms are selected from the group consisting of Clostridium, Moorella, Oxobacter, Peptostreptococcus, Acetobacterium, Eubacterium and Butyribacterium. 15. Method according to claim 6 or 7, characterized in that one or more microorganisms are selected from the group consisting of Clostridium autoethanogenum and Clostridium ljungdahlii. 16. Method according to claim 6 or 7, characterized in that at least one product is selected from the group consisting of ethanol, acetic acid and 2,3-butanediol.

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